8.2 System Variables Controlling the Trace

A brief overview from "mysqld --verbose --help":

--optimizer-trace=name
Controls tracing of the Optimizer:
--optimizer-trace-features=name
Enables/disables tracing of selected features of the
Optimizer:
optimizer_trace_features=option=val[,option=val...],
where option is one of {greedy_search, range_optimizer,
dynamic_range, repeated_subselect} and val is one of {on,
off, default}
--optimizer-trace-limit=#
Maximum number of shown optimizer traces
--optimizer-trace-max-mem-size=#
Maximum allowed cumulated size of stored optimizer traces
--optimizer-trace-offset=#
Offset of first optimizer trace to show; see manual
--end-markers-in-json=#
In JSON output ("EXPLAIN FORMAT=JSON" and optimizer
trace), if set to 1, repeats the structure's key (if it
has one) near the closing bracket